Sign in to follow this  
Followers 0
binsinkm

Ladder diagram

4 posts in this topic

Dear guys, If anyone knows how to make a ladder diagram for measuring speed (RPM) of a rotating shaft (turbine). Here, a magnetic pickup pulse is connected nearby the shaft and , which gives i/p s to the pulse to the PLC. (Suppose, 25 pulse means one rotation ). So, guys pls post here the ladder logic diagram for the above application.

Share this post


Link to post
Share on other sites
In general you want to use a self-resetting timer to copy the value out of a Counter accumulator every X number of seconds. Ordinary discrete inputs are not usually used for this sort of application, but it's possible to do so with relatively slow shaft speeds and relatively fast inputs, especially on the ControlLogix platform which has Change-of-State interrupts. How fast is your motor rotating ? For a typical 1800 RPM motor, at 25 pulses per revolution you're looking at 750 pulses per second. If the pulse is a 50% duty cycle (typical for an encoder) then your pulse is only 1/1500 of a second long. Can your discrete input module detect such a short pulse ? Can your controller handle being interrupted 1500 times per second to handle counting that pulse ? If you are really measuring motor speed, it would be better to use a dedicated purpose high-speed counter module, or even a frequency/analog converter.
1 person likes this

Share this post


Link to post
Share on other sites
Thank you for your kind response to the post. Actually, the shaft speed is between 3250 and 2750. Yes sir, i am looking for a a self-resetting timer to copy the value out of a Counter accumulator every X number of seconds. Actually iam not sure that the controller can track the 1500 pulses per second. Can you plz show me the ladder diagram for the above application (suppose the controller can handle it).

Share this post


Link to post
Share on other sites
You posted this into the Allen-Bradley section of this Forum, but you did not specify which model of Allen-Bradley controller you are using. Some of them have built-in high speed counters (MicroLogix) or specific module features that would help with this application (SLC-500 discrete input interrupt). I don't know of any general-purpose logic controller that can reliably count a pulse train at 1350 Hz without having an on-module counter. I am attaching a screenshot of a very basic counter and timer relay ladder logic routine to calculate RPM. It will not work for your application, but it should give you an idea of the basic logic necessary to do such a function with a slower signal.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0